This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-033932, filed Feb. 12, 1999; No. 11-318127, filed Nov. 9, 1999; and No. 11-319687, filed Nov. 10, 1999, the entire contents of all of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a plasma display panel, and to the method and apparatus for manufacturing the plasma display panel. In particular, the present invention relates to a plasma display panel which is provided with barrier ribs for partitioning the discharge region of the plasma display panel, and to the method and apparatus for manufacturing such a plasma display panel.
2. Description of the Related Art
Conventionally, a CRT has been extensively employed as an image display device. However, the CRT is defective in the respects that it is large in overall size and weight, and that it requires a high voltage. Under the circumstances, a flat type image display device such as a light emitting diode (LED), a liquid crystal display device (LCD), a plasma display panel (PDP), a plasma addressed liquid crystal display (PALC), etc. has been developed in recent years, and these devices are now increasingly utilized.
Among them, due to the propagation of multimedia, the plasma display panel which is adapted to be employed as an interface of information in a color display device of large image area is now noticed as promising because the structure thereof where the emission of plasma is utilized is simple, it is suited for achieving a large image area and an excellent image quality, it is light in weight, and it is thin-walled so that it is free from restriction regarding the installation place thereof.
This plasma display panel comprises discharge display cells having minute spaces which are encircled by barrier ribs partitioning a space formed between a pair of flat insulating substrates, wherein each of the discharge display cells is provided therein with a pair of discharge electrodes and an address electrode which is disposed at the bottom of the discharge display cell. The minute spaces of the discharge display cells are formed of an air-tight structure filled therein with a dischargeable gas such as a rare gas, thereby enabling a plasma to be generated in the spaces through the discharging between the discharge electrodes and the address electrode, wherein the switching of light emission of the discharge display cells is effected by the address electrode.
The plasma can be generated by selectively applying a voltage between facing discharge electrodes, and vacuum ultraviolet rays released from the plasma are utilized for generating light from the phosphors formed within the discharge display cells, thereby making it possible to utilize the discharge display cells as the light-emitting elements of image display device.
Therefore, it is required, for the performing the aforementioned switching, to apply a voltage between the discharge electrodes. However, if the electrostatic capacity of the discharge display cell is large, the driving current between the discharge electrodes is rendered to be increased. As a result, the power consumption of the plasma display panel is required to be increased, thereby raising a problem that the power source equipment of the plasma display panel is required to be enlarged.
Further, although the plasma display panel constructed as described above is simple in structure, and suited for enhancing the fineness of image, each of the electrodes and phosphors disposed inside the discharge display cells is permitted to be exposed directly to the plasma being generated. As a result, due to the sputtering effect of the plasma, the surfaces of these electrodes and phosphors are deteriorated, thereby raising a problem that the light emission efficiency of the display panel is liable to be decreased.
With a view to overcome these problems, there has been proposed a plasma display panel wherein a dielectric layer is formed on the opposing electrodes disposed inside the discharge display cell to thereby protect the surface of each electrode with this dielectric layer, thereby making it possible to reduce the electrostatic capacity of the discharge display cell and to prevent the electrodes and phosphors from being deteriorated by the plasma generated (Jpn. Pat. Appln. KOKAI No. H8-77930; and Jpn. Pat. Appln. KOKAI No. H7-57630).
As for the method of forming a dielectric layer of uniform thickness on the address electrodes of discharge display cell, there is generally known a method wherein a dielectric paste is printed, and the uniformity of thickness and the flatness of the printed layer are enabled to be achieved through the leveling effect of the surface of printed paste.
However, even if a dielectric paste of low fluidity is employed, with a view to ensure a uniform thickness and flatness of a dielectric layer, for forming a dielectric layer having a thickness of about 5 xcexcm on an electrode pattern ordinarily having a thickness of about 10 xcexcm, the surface of the dielectric layer to be obtained would become wavy due to the recessed and projected surface constituted by regions where the electrode pattern is existed and regions where the electrode pattern is not existed, thereby making it difficult to obtain a dielectric layer which is uniform in thickness.
On the other hand, if a dielectric paste having a high leveling property, i.e. excellent in fluidity is employed with a view to ensure the flatness of dielectric layer, it would become difficult to secure a sufficient thickness of the dielectric layer as it is formed on the address electrode, thereby possibly permitting part of the address electrode to be exposed to the outside. Thus, the thickness of the dielectric layer would become non-uniform, thus making it very difficult to obtain a dielectric layer which is uniform in thickness and excellent in flatness.
Therefore, since the thickness or flatness of the dielectric layer formed on the surface of address electrode becomes non-uniform as mentioned above, the quantity of electric charge to be stored in the dielectric layer is caused to differ depending on the regions thereof. As a result, a voltage for controlling the emission of light is caused to differ for each of the discharge display cells depending on the location thereof, thereby raising a problem that it is impossible for the address electrode disposed between the barrier ribs to display a stable and accurate light emission.
Furthermore, the forming of the dielectric layer by means of printing method leads to an increase in number of steps by one additional step in the manufacture of the back plate of plasma display panel. Furthermore, since the material for forming the barrier rib differs from the material for forming the dielectric layer, there is a room for improvement not only in terms of productivity but also in terms of material cost.
There has been also proposed, as a method of forming the barrier rib integral with the dielectric layer, a press molding method wherein the material for forming the barrier rib is press-molded by making use of an intaglio having a pattern of the barrier ribs. Although it is required, in this case, to control the thickness of the dielectric layer through the adjustment of gap between the intaglio and the substrate, the provision of the gap makes it difficult to obtain a sufficient pressing pressure, and still more, it is difficult to precisely fit the barrier rib-forming material into the aforementioned intaglio of barrier rib-like configuration.
Additionally, the provision, in advance, of the thickness-wise configuration of the dielectric layer in the intaglio is difficult in the aspect of working the intaglio. Further, if there is a wavy portion in thickness-wise in the glass substrate or any non-uniformity in the pressing pressure to the intaglio, it becomes difficult to make constant the gap between the intaglio and the substrate, thus failing to obtain the dielectric layer having a uniform thickness.
The barrier ribs for constituting the discharge display cell are formed of an insulating material, e.g. an inorganic metal oxide, in general, which is bound by lead glass. As for the specific method of fabricating the barrier rib, there are known various method. At present however, the sand blast method is mainly employed (as for the conventional method of fabricating the barrier rib, see a monthly publication; Kameya, xe2x80x9cLCD intelligencexe2x80x9d, August 1997, pp 57).
This sand blast method is featured in that a barrier rib-forming material is coated on a substrate to a predetermined thickness, and after predetermined regions of the coated layer which are desired to be left have been masked, sand is blasted onto the coated layer to thereby cut away redundant portions of the barrier rib-forming material, thereby forming a barrier rib.
Generally, barrier ribs, dielectric materials and electrodes, which are constituent elements for the discharge display cell, are formed on the back substrate.
According to the conventional manufacturing process, a back substrate as shown in FIG. 1 is manufactured by a sequence of steps, i.e. (1) a step of forming electrodes 2 on a glass substrate 1; (2) a step of forming a dielectric layer 3 on the surface of the electrodes 2; and (3) a step of forming barrier ribs 4 on the surface of the dielectric layer 3 (i.e. the electrodes 2xe2x86x92the dielectric layer 3xe2x86x92the barrier ribs 4).
Since each of these steps accompanies a substrate-sintering step, the dimension of the substrate is caused to vary on every occasions of these steps.
Therefore, when a strict dimensional accuracy is demanded for the purpose of enhancing the fineness of display cells, a problem is raised in the respect that the alignment between the electrodes and the barrier ribs becomes increasingly difficult due to the dimensional changes of substrate resulting from the sintering of the substrate.
Further, when the pitch of pixel becomes narrower, a defective such as short circuit between electrodes in the step of forming electrodes is liable to be generated, thus raising a problem.
By the way, although the barrier ribs are generally formed as an independent column, respectively, it is increasingly demanded to make the width of barrier rib narrower in order to increase the aperture ratio as the display is required to be further enhanced in fineness and in precision.
In this case, a problem is raised in that when the barrier ribs are formed into an independent column, respectively, the narrower the width of barrier rib becomes, the more it becomes likely that the barrier rib tends to fall down.
When it is desired to enhance the luminescence intensity of each pixel, it can be realized by enhancing the luminescence intensity of the phosphor itself. Alternatively, the light to be emitted from the phosphor may be reflected so as to increase the quantity of light to be emitted outside.
In order to realize this, it is preferable that the barrier rib to be formed on the back substrate is produced by making use of a white material which is excellent in reflectivity, and at the same time, a white dielectric material is formed also on the electrodes interposed between the barrier ribs, thereby enhancing the reflectivity of the substrate as high as possible.
Further, the thickness of the dielectric material should preferably be such that the permeation of visible light to the rear surface of substrate can be inhibited.
However, the thickness of the dielectric material will be restricted by the driving voltage, i.e. when the thickness of the dielectric material is increased, the driving voltage will be required to be proportionally increased. In view of this problem, the thickness of the dielectric material is in the range of 10 to 15 xcexcm in general.
Accordingly, there is a problem that it is impossible, according to the plasma display that has been manufactured by making use of the aforementioned back substrate, to obtain a satisfactory brightness, because most of emitted light is permitted to permeate toward the rear surface of the back substrate.
On the other hand, as for the thin display apparatus of large image area, a 25-inch plasma addressed liquid crystal display is placed on the market, and a 42-inch plasma addressed liquid crystal display is also exhibited in an exhibition (S. Fukusue; xe2x80x9cManufacturing Process of PALCxe2x80x9d, a monthly publication, xe2x80x9cFPD intelligencexe2x80x9d, vol. 6 (1998), pp 79-83).
In the manufacture of the plasma addressed liquid crystal display panel which is actually employed as described above, a process mainly utilizing a thick film printing method as disclosed in Jpn. Pat. Appln. KOKAI No. H4-265931 is adopted, thereby making it suited for the mass-production as well as for the production of panel having a large image area.
FIGS. 2 and 3 illustrate one example of this conventional plasma addressed liquid crystal display panel. As shown in FIGS. 2 and 3, after an anode 11 and cathode 12 are formed on the surface of a plasma substrate 10, barrier ribs 13 are formed on the substrate 10. Thereafter, the resultant body is sealed by making use of a dielectric thin glass plate 14 and by way of frit glass sealing. After this sealed body is evacuated, a discharge gas is introduced therein. After a CF layer 16 consisting of R, G and B, and a black stripe 17 are successively formed on a CF substrate 15, a signal electrode 18 is formed thereon. Then, the plasma substrate 10 and the CF-attached glass substrate 15 are arranged to oppose to each other with a spacer being interposed therebetween, and then, a liquid crystal 19 is further introduced thereinto. Finally, a polarizing plate 20 and a back light 21 are disposed in place to accomplish the fabrication of the plasma addressed liquid crystal display panel.
Next, the structure of the conventional plasma addressed liquid crystal display panel which is related to the present invention as well as the manufacturing method thereof will be explained with reference to FIG. 3 where the structure of the panel is shown and to FIG. 4 where the manufacturing steps of the panel are shown. By the way, in the case of a 42-inch plasma addressed liquid crystal display panel, the pitch of barrier ribs is set to 1.092 mm.
First of all, a low expansion coefficient glass substrate provided with an exhaust pipe-connecting hole is washed and dried. Then, by means of screen printing method, a Ni electrode paste is coated on the entire surface on the structure and then, dried to form a Ni electrode layer having a thickness of 50 xcexcm. The Ni electrode paste in this case is mainly composed of a Ni metal powder, a low melting point glass, an antioxidant, a binder resin which is excellent in pyrolizability (ethyl cellulose, etc.), and a solvent for providing an excellent rheological property for screen printing (butyl acetate carbitol, xcex1-terpineol, etc.). Thereafter, a dry film (DF) is adhered onto the electrode layer, and patterned by way of exposure and development. Then, by means of sand blast method, redundant portions of the Ni electrode material are removed and the DF is peeled away. As a result, a stripe-shaped Ni electrode pattern corresponding to the anode and cathode for a discharging space is obtained. Further, since it is difficult to perform a vacuum sealing in this structure having the Ni electrode, a Ag electrode paste is further coated, by means of screen printing method, for use for the sealing portion and for the terminal electrode portion. By the way, for the purpose of preventing the generation of abnormal discharging at an end portion of plasma channel, a cover glass paste is coated by means of screen printing.
Thereafter, a barrier rib-forming paste for forming a barrier rib of plasma cell is repeatedly coated and dried several times by means of screen printing method until the resultant laminated structure becomes as high as about 250 xcexcm in thickness, the resultant paste layer being subsequently baked. The barrier rib-forming paste in this case is mainly composed of a low melting point glass, a binder resin which is excellent in pyrolizability (ethyl cellulose, etc.), a solvent for providing an excellent rheological property for screen printing (butyl acetate carbitol, xcex1-terpineol, etc.), and a black pigment. By the way, the purpose for adding a black pigment to the barrier rib-forming paste is to make the barrier rib black in color after the sintering thereof and hence to prevent light from being reflected from the sidewall of barrier rib as explained below. Finally, the top portion of the barrier rib is polished so as to control the height of barrier rib to 200 xcexcmxc2x12 xcexcm and to flatten the top surface of barrier rib. Thereafter, the barrier rib is fully washed so as not to leave any residual materials after the polishing. By the way, the dimension of the Ni electrode after the sintering of the barrier rib is about 40 xcexcm in thickness and about 100 xcexcm in width. Further, the resistance of the barrier rib with about 1000 mm of the discharge portion thereof is about 500 xcexa9.
Since this Ni electrode is not formed of pure metal but formed of a glass cermet consisting of a metal and a low melting point glass frit, the electric resistance after sintering is at least 20 times as high as that of metal Ni. Therefore, the electrode cannot be made narrower in width and thinner in thickness. Since the width of the electrode cannot be made narrower, the aperture ratio cannot be reduced, thereby deteriorating the utilization efficiency of light emitted from the back light. Further, since the aperture ratio becomes 40% or less, it will become a decisive defect for the barrier ribs whose pitch is set to 0.485 mm as in the case of the 42-inch HDTV specification.
Further, since the thickness of the Ni electrode after the sintering thereof is set to about 40 xcexcm, it will become difficult to uniformly laminate a dry film (DF) on the surface of the substrate. As a result, it becomes difficult to employ a paste-burying method wherein the height and configuration of the top of the barrier rib can be easily controlled by adjusting the thickness of the DF.
On the other hand, the method of forming the barrier rib by means of a sand blast method which has been proven to be useful for mass production in the method of forming the barrier rib of an AC type plasma display panel (PDP) is advantageous in that since the electrodes of plasma display panel are covered with a dielectric layer, the electrodes can be prevented from being damaged by the sand blast on the occasion of forming the barrier rib. However, since the electrodes are left exposed in the case of the PALC, the electrodes may be damaged by the sand blast, and hence this method is not so suited for use, and in fact, this method is not actually employed.
Under the circumstances, the screen printing method which is somewhat defective in terms of dimensional precision is compelled to be employed in the production of the barrier rib. In this case, if the pitch of the barrier ribs is set to 1.092 mm as in the case of the 42-inch VGA specification, a sufficient margin can be secured, thereby making it possible to form the barrier rib between electrodes. However, if the pitch of the barrier ribs is to be set to 0.485 mm as in the case of the 42-inch HDTV specification, an alignment precision within the range of xc2x110 xcexcm is required, and hence this method is decisively defective in this respect.
As explained above, black barrier ribs are employed in the conventional structure of display panel. The purpose of providing the black barrier ribs is to suppress the influence of the deterioration of contrast that will be induced by the stray light which is reflected from the sidewall of the barrier rib. As a result, the light is shielded by the black barrier ribs and hence the aperture ratio is restricted, thus inviting a decisive defect that it is difficult to enhance the utilization efficiency of the backlight.
There is another problem that even if a liquid crystal of wide viewing angle mode is employed, the advantages thereof cannot be fully utilized due to so-called louver effects where the viewing angle is restricted in the direction perpendicular to the black barrier rib. With a view to overcome this problem, Jpn. Pat. Appln. KOKAI No. H11-212068 proposes a novel structure of plasma addressed liquid crystal display panel where the following measures are adopted.
Transparent barrier ribs are formed in place of the aforementioned black barrier ribs. It is possible, with this structure, to prevent the narrowing of viewing angle to be induced by the louver effects. When the transparent barrier ribs are formed of a material whose surface is relatively smooth, the deterioration of contrast due to the scattering of light can be suppressed. Further, if it is constructed such that the polarizing plate arranged close to the back glass substrate is disposed in such a manner that the direction of transmission axis thereof is oriented at an angle of 0 degree or 90 degrees to the direction of the transparent barrier rib; that the polarizing plate arranged close to the front glass substrate is disposed in such a manner that the direction of transmission axis thereof is oriented orthogonal to the transmission axis of the polarizing plate arranged close to the back glass substrate; and that the transparent barrier ribs are erected perpendicular to the back glass substrate, the rotation of light on polarization plane can be prevented on the occasion when the light passes through the transparent barrier rib.
It is said that as a result of the structure as mentioned above, it becomes possible to obtain a panel which is excellent in utilization efficiency of backlight, without deteriorating the contrast, and wide in viewing angle as compared with the conventional panel having the black barrier ribs.
However, this manufacturing method of the back glass substrate is substantially the same as the aforementioned method of manufacturing the barrier rib substrate of plasma addressed liquid crystal display by means of the conventional thick film printing method. Namely, this manufacturing method is simply featured in that a glass paste for forming a transparent barrier rib is substituted for the glass paste for forming a transparent barrier rib. Therefore, this manufacturing method is accompanied with the same decisive defect as mentioned above.
Further, as apparent from the aforementioned manufacturing technique of plasma display, the conventional method of forming the barrier rib through a repetition of the thick film printing method is accompanied with a problem that in what manner the rheological property of the barrier rib-forming paste is controlled, it is unrealistic, even if it may be possible in the level of laboratory, to vertically erect the barrier rib up to a height of as high as 250 xcexcm on the surface of glass substrate. It is much less possible to uniformly erect vertical barrier ribs up to a height of as high as 250 xcexcm on the surface of glass substrate of 42 inches in size. Additionally, it is difficult to take measures to a problem of stepped portions which may be formed on the sidewall of barrier rib due to the repetition of the printing procedure.
As mentioned above, there has been proposed, as a method of forming the barrier rib integral with the dielectric layer, a method of press-molding a material for the barrier rib by making use of an intaglio having a configuration of the barrier rib. This method of forming a projection pattern by making use of such an intaglio is accompanied with the following problems as explained below.
A first problem to be raised on the occasion of forming a projected pattern on a rigid substrate by making use of an intaglio is that since the intaglio is also formed of a rigid material, an insufficiently contacted portion may be generated at the interface between the intaglio and the rigid substrate. As a result, the transfer of ink from the intaglio to a printing matter (matter to be printed) this insufficiently contacted portion, thereby generating a defective portion indicating a transfer failure. Jpn. Pat. Appln. KOKAI No. H4-34551 discloses a method for overcoming this problem. This method is directed to the transfer of a pattern to a glass substrate, etc., wherein an ink-repellent elastic layer is formed all over the surface of the intaglio excluding the recessed portions thereof. At the time of printing, this elastic layer is deformed by the printing pressure, thereby enabling the elastic layer to be closely contacted with a rigid substrate such as a glass substrate which may be non-uniform in thickness or uneven in surface state, thus permitting ink to transfer from the intaglio to the substrate. As a result, a pattern which is minimal in defects is said to be obtained.
Though it may depend on the viscosity of ink, ink is caused to split at approximately half a depth of the intaglio at the transferring step thereof, so that a projected pattern to be obtained is of reduced thickness. Additionally, the configuration of the projected pattern thus obtained is also influenced by the splitting of ink.
Meantime, Jpn. Pat. Appln. KOKAI No. S57-87318 discloses a method for preventing the generation of the splitting of ink. Namely, this method is featured in that the ink (paste) to be employed therein is formed of an ultraviolet-curing composition or of an electron beam curing composition, and hence the ink held in the intaglio is preliminarily cured before it is transferred. It is also disclosed therein that for the purpose of enhancing the releasability of intaglio, silicone is applied to the interior of intaglio.
Further, Jpn. Pat. Appln. KOKAI No. H4-35989 discloses a method which seems to be a modification of the method disclosed in Jpn. Pat. Appln. KOKAI No. H4-34551. Namely, this method is featured in that the inner surface of the recessed portions is constituted by a releasable material such as silicone rubber or Teflon, thereby improving the transferability of ink. Therefore, if an adhesive layer is deposited in advance on the surface of a rigid printing matter such as a glass substrate, the transfer of ink can be performed after the curing of ink, thereby enabling to obtain a projected pattern exhibiting an excellent configuration.
However, there is a problem that since the inner surface of the recessed portions is constituted by an ink-repellent surface or by a releasable surface, the ink that has been once introduced into the recessed portions may be removed from the recessed portions and adhered to an inking roller, as the inking roller is separated away from the intaglio.
The technique disclosed in this Jpn. Pat. Appln. KOKAI No. H4-35989 is a modification of the printing plate and of the printing method disclosed in Jpn. Pat. Appln. KOKAI No. S56-137989. According to the latter publication, the surface of printing plate is not provided with an ink-repellent layer, but is constituted by a hard material such as a chrome plating layer or a stainless steel plate. In this case, even if the inner surface of the recessed portions is poor in conformability with ink, it has been possible to enable the inner surface of recessed portion of the hard layer to become compatible with ink and hence to perform the inking, provided that the inking is performed by making use of a doctor blade. Since the backing material is expandable, the backing material is capable of pushing out ink as it is pressed, so that the transfer of ink to the rigid substrate can be performed without raising any serious problem. Further, since the ink can be cured before it is discharged from the printing plate so as to shape the ink into a desired configuration, it has been possible to push out the resultant cured ink toward a printing matter as mentioned above. However, it has been impossible to apply an adhesive material to the surface of printing matter in the transfer of ink to the printing matter, because if an adhesive material applied to the surface of printing matter, the printing plate will be bonded to the printing matter.
If silicone resin or fluororesin is applied, for the purpose of avoiding the aforementioned problem, to the surface of printing plate so as to make the surface of printing plate releasable to ink or an adhesive material, there will be raised another problem that since these resins are soft, these resins are liable to be damaged on the occasion of scraping out ink by means of doctor blade, and hence the durability of the printing plate becomes poor.
Jpn. Pat. Appln. KOKAI Nos. H4-10936 and H5-241175 set forth a method for modifying the aforementioned inking method. Namely, this method is featured in that ink is pushed into the recessed portions by making use of a film exhibiting an excellent releasability. According to this method, irrespective of whether the ink in the recessed portions is cured or not, there is no possibility that the ink in the recessed portions is wiped out or taken up by the inking roll.
However, these Japanese Patent Publications simply set forth the methods of inking and curing, but nothing about the apparatus thereof. Further, there is another problem which may be raised on the occasion of inking to the recessed portions. Namely, the problem is the entrapment of air bubbles, which is more likely to occur as the depth of the recessed portions becomes deeper, the pattern becomes finer, the viscosity of ink becomes higher, and the filling speed becomes faster. The aforementioned Japanese Patent Publications however suggest nothing about these problems.
Next, the method of continuously manufacturing the barrier ribs of flat plasma display panel using a rotary type apparatus type will be explained. As for the prior art, Jpn. Pat. Appln. KOKAI Nos. H8-321258 and H10-101373 set forth a technique related to this.
The method disclosed in Jpn. Pat. Appln. KOKAI No. H8-321258 will be explained with reference to FIGS. 5 to 7, wherein the following two steps are essentially required.
(1) By making use of an intaglio 54 provided with recessed portions 71 for forming the barrier rib portions of plasma display panel, an ionizing radiation-curing resin 53 containing glass frit is filled at least in the recessed portions 71 of the intaglio 54, and at the same time, a film substrate 61 is permitted to contact with the intaglio 54, during which an ionizing radiation 51 is irradiated to the ionizing radiation-curable resin 53 which is kept interposed between the film substrate 61 and the intaglio 54 to thereby cure the resin 53, after which the film substrate 61 and the resin 53 are released away from the recessed portions 71.
(2) The surface of ionizing radiation-curable resin thus cured, having the configuration of barrier ribs and formed on the film substrate 61 is closely contacted with the surface of the substrate of plasma display panel, and then, subjected to a sintering step.
Namely, for the purpose of obtaining a desired configuration of barrier ribs, this desired configuration is formed on a film substrate at first in the step (1); and then, the configuration formed on a film substrate is transferred to a glass substrate.
The aforementioned manufacturing method is accompanied with the following problems.
(1) Since the configuration of barrier ribs is formed on a film at first, and then, the configuration of barrier ribs is transferred, it is very difficult to secure the positional precision (dimensional precision). Because the barrier ribs are required to be aligned with an electrode to interposed between these barrier ribs, and a positional precision of about xc2x12-10 xcexcm/m is required.
Referring to FIG. 5, the longitudinal direction of the barrier ribs is orthogonally intersected with the longitudinal direction of the film. Accordingly, if the barrier ribs are to be formed in the direction shown in FIG. 5, the precision of the barrier ribs is directly influenced by the shrinkage and expansion of the film, so that in the case of polyester film to be employed in the example for example, the expansion of the polyester film is required to be adjusted through a precise tension control in the longitudinal direction thereof on the occasion of transferring to thereby adjust the pitch of the barrier ribs.
Further, even if the barrier ribs are to be formed in the orthogonally intersecting direction as shown in FIG. 5, i.e. in the direction where the longitudinal direction of the barrier ribs is coincide with the longitudinal direction of the film, a precise tension control in the lateral direction thereof is required. In this case, the tension control in the longitudinal direction of the film is also required for preventing the generation of defects such as a disconnection of barrier ribs, etc. It is also difficult to carry out the winding of film. As shown in FIG. 6, the film should most preferably be disposed flat after finishing the transferring of the barrier ribs on the film.
(2) Although the configuration of the barrier rib should preferably be trapezoidal as it is viewed from the back substrate side, if the configuration of the barrier rib is such as shown in FIGS. 6 and 7, the configuration of the corresponding portions of the intaglio would be such that it is tapering in the direction toward the surface thereof. As a result, it would become very difficult to release a cured barrier rib portion from the intaglio. By the way, the configuration that can be easily released from the intaglio is a reversed trapezoid.
(3) A problem which will be raised also in this method is the entrapment of air bubbles. However, the aforementioned publication is silent about this problem.
On the other hand, Jpn. Pat. Appln. KOKAI No. H10-101373 sets forth a very comprehensive and conceptual method, and the method of the present invention is included in part in the method of this Publication H10-101373. FIG. 8 shows a drawing which is also shown in this Publication H10-101373.
This patent publication mentions that it includes not only a rotary system but also a flat system, either of which however are already disclosed in the aforementioned publications.
In conclusion, this publication simply sets forth a gathering of known methods except that it discloses the employment of a thermoplastic resin. Further, nothing is insisted in this publication about any prominent effects to be obtained from a specific combination of known methods.
Almost nothing is known about a specific embodiment of apparatus which is useful for actually realizing these conventional methods. Basic reasons for this may be ascribed to the problems that some of them are excellent as an idea but are difficult to actually realize, some of them fail to disclose a specific means for securing the accuracy, and some of them are poor in durability.
For example, as for the method of scraping out a redundant portion of ink from the roll supplied with the ink, Jpn. Pat. Appln. KOKAI No. H10-101373 proposes to employ a member called doctor as shown in FIG. 8. However, when such a method is adopted for removing a redundant portion of ink, the surface of intaglio would be abraded and damaged with time unless the surface of the roll is very hard and excellent in slip properties. Therefore, it is required in a gravure printing to employ a metal roll having a chrome-plated surface. The employment of a plastic roll is also conceivable as an idea and may be advantageous in various aspects, but is too poor in hardness, thus permitting it to be easily abraded, so that a plastic roll is not actually employed.
Further, Jpn. Pat. Appln. KOKAI No. H10-101373 fails to teach anything about the surface hardness and abrasion resistance of the roll. However, according to examples thereof, a silicone rubber type roll which is made of a room temperature curing silicone (RTV141) is employed therein. However, since the rubber hardness of RTV is 100 at most, the silicone rubber type roll seems to be very questionable in terms of durability. On the other hand, if the intaglio is very hard, it would be impossible to perform a printing on a rigid substrate such as a glass substrate.
The present invention has been accomplished in view of the aforementioned circumstances, and therefore, a first object of the present invention is to provide a plasma display panel and a manufacturing method thereof, which make it possible to easily obtain a large image area of 40 inches or more, to realize an increased fineness of discharge display cell, to obtain a stable and accurate luminescence display, and to enhance the durability thereof.
A second object of the present invention is to provide a plasma display panel which is provided with barrier ribs which can be hardly collapsed even if the width thereof is minimized, and which makes it possible to minimize the leak of luminescence light toward the rear side of the back substrate, to accurately set the alignment between the electrodes and the barrier ribs, and to prevent the generation of disconnection or short circuit of electrodes.
A third object of the present invention is to provide a plasma addressed liquid crystal display panel structure and a manufacturing method thereof, which make it possible to erect transparent barrier ribs perpendicular to a glass substrate, and to produce the transparent barrier ribs having a smooth sidewalls.
A fourth object of the present invention is to provide a method and an apparatus, which is suited for mass-production, and which make it possible to form a thick projected pattern directly onto a rigid substrate with excellent reproducibility by way of intaglio-rotating system.
According to a first embodiment of a first aspect of the present invention, there is provided a plasma display panel comprising:
a back substrate;
barrier ribs arranged on the back substrate;
electrodes each formed in a region partitioned by the barrier ribs; and
a dielectric layer covering the electrodes;
wherein the barrier ribs and the dielectric layer comprise the same barrier rib-forming material containing a low melting point glass frit.
According to a second embodiment of the first aspect of the present invention, there is provided a method of manufacturing a plasma display panel, which comprises the steps of:
filling a barrier rib-forming paste containing glass frit in a barrier ribs-forming intaglio;
superimposing a substrate on the barrier ribs-forming intaglio filled with the barrier rib-forming paste containing glass frit to thereby transfer the barrier rib-forming paste onto the substrate; and
heating the barrier rib-forming paste which is transferred to the substrate, thereby burning out existing organic components and concurrently sintering the glass frit to thereby form the barrier ribs and dielectric layer.
The followings are preferable embodiments of this first aspect of the present invention.
(1) The film thickness of the dielectric layer is in the range of 5 to 50 xcexcm.
(2) The film thickness of the dielectric layer is in the range of 5 to 20 xcexcm.
(3) The dielectric layer has a two-layer structure comprising a barrier rib material layer, and a low melting point glass paste layer which differs in material from the barrier rib material.
(4) The film thickness of the dielectric layer is in the range of 5 to 20 xcexcm, and the dielectric layer has a two-layer structure comprising a barrier rib material layer, and a low melting point glass paste layer which differs in material from the barrier rib material.
(5) A barrier rib-forming paste containing glass frit is filled in a barrier ribs-forming intaglio, and a dielectric layer having a predetermined thickness is concurrently formed on the intaglio, the dielectric layer being subsequently transferred onto the substrate.
According to a second aspect of the present invention, there is provided a plasma display panel comprising:
a back substrate; and
barrier ribs arranged on the back substrate;
electrodes each formed in a region partitioned by the barrier ribs;
wherein the barrier ribs have a recessed structure comprising a bottom structure contacting with the back substrate, and an upper structure projected from the bottom structure; and the electrodes are each disposed at the bottom of the recessed structure.
According to the second aspect of the present invention, since the dielectric layer disposed at the bottom of discharge display cell which is surrounded by the back substrate and the barrier ribs formed integral with the back substrate can be optimized in thickness thereof to thereby make it possible to obtain the dielectric layer of uniform thickness, the quantity of electric charge of the dielectric material constituting the dielectric layer can be made uniform, thereby making it possible to realize a stable and accurate luminescence display.
Further, since the dielectric material constituting the dielectric layer is the same as the material constituting the barrier ribs, and additionally, since the dielectric layer can be formed concurrent with the formation of the barrier ribs, the productivity can be enhanced and the manufacturing cost can be saved in the manufacture of the substrate for plasma display.
The followings are preferable embodiments of this second aspect of the present invention.
(1) The visible light reflectivity of the regions other than the electrodes is 50% or more, more preferably 70% or more under the condition where a phosphor is not coated.
(2) A recessed portion is formed at the bottom of the opening portion of the recessed structure, and the electrode is disposed at this recessed portion.
(3) The width of the recessed portion is the same in size as the bottom of the opening portion of the recessed structure.
(4) The electrode is formed of a metal wire or a metal plate.
(5) The thickness of the bottom of the recessed structure is larger than the width of the upper structure of the recessed portion.
(6) The thickness of the bottom of the recessed portion which is formed at the bottom of the opening of the recessed structure is larger than the width of the upper structure of the recessed portion.
(7) A dielectric layer is formed at the bottom of the recessed structure, and a total of the thickness of the bottom structure of the recessed structure and the thickness of the dielectric layer is larger than the width of the upper structure of the recessed portion.
According to a first embodiment of a third aspect of the present invention, there is provided a back plate of plasma addressed liquid crystal display panel comprising:
a back substrate;
a transparent dielectric layer formed on the back substrate;
transparent barrier ribs arranged on the transparent dielectric layer and comprising the same material as that of the transparent dielectric layer;
an anode formed on the transparent dielectric layer; and
a cathode formed on the transparent dielectric layer.
The followings are preferable examples of a first embodiment according to the third aspect of the present invention.
(1) The film thickness of the transparent dielectric layer is in the range of 3 to 15 xcexcm.
(2) The angle between the sidewall of the transparent barrier rib and the back substrate is in the range of 85 to 95 degrees.
(3) The surface roughness of the sidewall of the transparent barrier rib is within 1 xcexcm and is equivalent almost to an optical flat surface.
(4) The anode and the cathode comprise the same material.
(5) The anode and the cathode comprises a thick film or a plated film, each containing 80% or more of Ni.
(6) The anode and the cathode comprises a thick film or a vapor-deposited film, each containing 80% or more of Al.
(7) Among the anode and the cathode, at least cathode has a two-layer structure.
(8) A back plate of the plasma addressed liquid crystal display panel claimed in any one of claims 16 to 19.
(9) The anode and the cathode comprise the same material having a photosensitivity, and employed respectively as an underlying electrode, and at least the cathode is provided thereon with a protective plating having a sputter resistance against the cation of discharging gas and containing 80% or more of Ni.
(10) The underlying electrode is formed by using a photosensitive Ag paste.
According to a second embodiment of the third aspect of the present invention, there is provided a method of manufacturing a back plate of plasma addressed liquid crystal display panel, which comprises:
coating a barrier rib-forming paste containing glass frit on a surface of substrate;
forming a pattern of barrier ribs by pressing the barrier rib-forming paste formed on the surface of substrate by making use of a barrier rib-forming intaglio;
heating the pattern of barrier ribs, thereby burning out existing organic components and concurrently sintering the glass frit to thereby form transparent barrier ribs and a transparent dielectric layer; and
forming a cathode and an anode on the transparent dielectric layer.
According to a third embodiment of the third aspect of the present invention, there is provided a method of manufacturing a back plate of plasma addressed liquid crystal display panel, which comprises:
filling a barrier rib-forming paste containing glass frit in a barrier ribs-forming intaglio, while concurrently enabling a dielectric layer having a predetermined thickness to be formed on the intaglio;
superimposing a substrate on the barrier ribs-forming intaglio filled with the barrier rib-forming paste to thereby transfer the barrier rib-forming paste onto the substrate to form a pattern of barrier ribs;
heating the pattern of barrier ribs, thereby burning out existing organic components and concurrently sintering the glass frit to thereby form transparent barrier ribs and a transparent dielectric layer; and
forming a cathode and an anode on the transparent dielectric layer.
The followings are preferable examples of the second and third embodiments according to the third aspect of the present invention.
(1) The anode and the cathode are formed by means of an electroless plating method.
(2) The anode and the cathode are formed by a procedure comprising: coating a thick film paste; coating a liquid photoresist; patterning the photoresist; forming an electrode pattern by means of sand blast; and sintering the electrode pattern.
(3) The anode and the cathode are formed by means of a photosensitive paste method.
(4) The anode and the cathode are formed by means of a vapor deposition method.
(5) Among the anode and the cathode, at least the cathode has a two-layer structure, and an underlying electrode of the two-layer structure is formed through an electrolytic plating using a material having a sputter resistance against plasma cation.
According to a first embodiment of the fourth aspect of the present invention, there is provided a recessed and projected pattern-forming apparatus of rotary type for forming a cured recessed and projected pattern of an ionizing radiation-curable resin composition on a rigid plate, the apparatus comprising:
an intaglio-rotating roll provided on the surface thereof with a predetermined recessed and projected pattern constituted by a releasable surface;
a pinching mechanism for enabling the ionizing radiation-curable resin composition to be continuously pinched between the intaglio-rotating roll and an ionizing radiation-permeable releasable film while keeping a predetermined thickness of the ionizing radiation-curable resin composition;
an radiation irradiating mechanism for irradiating an ionizing radiation to the resin composition under the aforementioned pinched condition;
a releasing mechanism for releasing the ionizing radiation-permeable releasable film from the surface of the intaglio-rotating roll after finishing the curing of the ionizing radiation-curable resin composition;
a press mechanism which is designed such that the rigid plate is fed over the intaglio-rotating roll for enabling the rigid plate to be superimposed and aligned, at a predetermined precision, with the ionizing radiation-curable resin composition which is cured by the ionizing radiation, and that the resultant composition thus aligned is placed into a compressed state; and
a releasing mechanism for enabling the rigid plate to be released from the surface of the intaglio-rotating roll after a termination of the compressed state.
According to a second embodiment of the fourth aspect of the present invention, there is provided a rotary type recessed and projected pattern-forming method for forming a cured recessed and projected pattern of an ionizing radiation-curable resin composition on a rigid plate, the method comprising:
continuously permitting the ionizing radiation-curable resin composition to be pinched between an intaglio-rotating roll and an ionizing radiation-permeable releasable film while keeping a predetermined thickness of the ionizing radiation-curable resin composition, the intaglio-rotating roll being provided on the surface thereof with a predetermined recessed and projected pattern constituted by a releasable surface;
irradiating an ionizing radiation onto the resin composition under the aforementioned pinched condition;
releasing the ionizing radiation-permeable releasable film from the surface of the intaglio-rotating roll after finishing the curing of the ionizing radiation-curable resin composition;
feeding the rigid plate over the intaglio-rotating roll for enabling the rigid plate to be superimposed and aligned, at a predetermined precision, with the ionizing radiation-curable resin composition which is cured by the ionizing radiation, and placing the resultant composition thus aligned into a compressed state; and
releasing the rigid plate from the surface of the intaglio-rotating roll after a termination of the compressed state.
The followings are preferable examples of the first and second embodiments according to the fourth aspect of the present invention.
(1) The surface of the intaglio-rotating roll comprises silicone resin.
(2) These embodiments further comprises a mechanism or step of preliminarily coating a self-adhesive or an adhesive onto the rigid plate to be fed over the intaglio-rotating roll.
(3) These embodiments further comprises a mechanism or step of coating a transferring resin onto the surface of the cured ionizing radiation-curable resin composition.
(4) The width of the ionizing radiation-permeable releasable film having a releasability is larger than the width of the intaglio-rotating roll.
(5) The mechanism or step of continuously permitting the ionizing radiation-curable resin composition to be pinched between an intaglio-rotating roll and an ionizing radiation-permeable releasable film while keeping a predetermined thickness of the ionizing radiation-curable resin composition is constituted by a mechanism or step wherein the ionizing radiation-curable resin composition is coated in advance on the surface of the ionizing radiation-permeable releasable film, and then, the film is superimposed with the intaglio-rotating roll.
(6) These embodiments further comprises a mechanism or step of preliminarily coating a self-adhesive or an adhesive onto the surface of the ionizing radiation-permeable releasable film.
(7) These embodiments further comprises a mechanism or step of feeding a liquid to a region where the intaglio-rotating roll begins to be in contact with the ionizing radiation-curable resin composition.
(8) These embodiments further comprises a mechanism or step of feeding a liquid to a region where the intaglio-rotating roll begins to be in contact with the rigid plate.
(9) The mechanism of transferring the rigid plate is constituted by an X-Y-xcex8 table having a mechanism of securing the rigid plate and designed to be moved following a guide rail.
(10) An alignment mark is attached to both of the intaglio-rotating roll and the rigid plate at their corresponding positions, thereby making it possible to transfer the alignment mark of the intaglio to the rigid plate, and to measure any misregistration between the alignment mark of the intaglio which is transferred to the rigid plate and the alignment mark of the rigid plate, thereby enabling the position of the X-Y-xcex8 table holding the rigid plate to be adjusted correspondingly so as to perform the alignment between the intaglio and the rigid plate.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.